The present invention relates to the fields of mechanics, thermodynamics, fluidics, refrigeration, dehumidification and water collection and purification. In particular, it relates to a device and method for preventing ice formation on the evaporator of a device operating in a refrigeration cycle, particularly at low ambient air temperatures.
The refrigeration cycle has numerous uses. One, of course, is refrigeration, the cooling of ambient air in an enclosure to a temperature at or below freezing for the purpose of preventing the spoilage of comestibles such as meat, fresh fruit and fresh produce. Another is building air conditioning. A further use for the refrigeration cycle is removing water from moist air. The purpose may simply be to dry the air as in the case of household dehumidifiers, industrial scale fruit and vegetable dryers and the like. Or the purpose may be to produce potable water for personal household use, camping, public water conservation and the like or for use during emergencies such as earthquakes, floods, fire and other natural disasters or man-made disasters such as war, when the normal water supply is compromised. In any event, the device and method employed is essentially the same and is schematically depicted in FIG. 1.
In FIG. 1, compressor 1 receives a refrigerant gas, such as ammonia, sulfur dioxide, Freon(copyright), and the like, and compresses it, i.e., raises its pressure. As the result of being compressed, the gas heats up, becoming a hot, high pressure gas. The hot, high pressure gas is then received by condenser 2, which consists of a heat exchanger having a large surface area that is in contact with circulating ambient air. The hot, high pressure gas surrenders some of its heat content to the circulating air and, as a result, is condensed to a liquid which, while still warm, is cooler than the hot gas entering the condenser. The warm, high pressure liquid then travels to metering device 3, which can be a simple orifice, a capillary tube or a thermostatic expansion valve, and which forces the liquid to expand and thereby cool further. The cool liquid then travels to evaporator 4, which, like the condenser, consists of a large surface area over which moisture-containing air can be circulated. The evaporator can be merely a length of tubing which has been folded over on itself in a serpentine manner as depicted in FIG. 1. Or the tubing can be flattened to provide more surface area when it is folded into a given volume of space. The tubing may also have vanes attached to provide more surface area. The evaporator can also be an interconnected hollow core honeycomb such as the radiator of an automobile. These and many other evaporator designs are well-known in the art. In any event, the cool liquid passing through evaporator 4 absorbs heat from the air in contact with the exterior surface of the evaporator and, when enough heat energy, called the heat of vaporization, has been absorbed, converts back into a gas, which is at approximately the same temperature as the cool liquid entering the evaporator, the heat absorbed having been used in the vaporization process. When the device is being used as a dehumidifier, the operating parameter of metering device 3 is such that the temperature of the cool, low pressure liquid circulating through the evaporator 4 is below the dew point of the air in contact with the exterior surface of the evaporator. The dew point is the temperature at which water vapor in air will condense. Thus, as the cool liquid circulates through the evaporator, absorbs heat from the surrounding air through the surface of the evaporator and vaporizes, water vapor-containing air in contact with the evaporator is cooled to below its dew point. Water vapor in the air then condenses on the evaporator and flows out of the system. The cool gas returns to the compressor to begin another cycle. A receiver is sometimes placed in the system between the condenser and the metering device to store the warm, high pressure refrigerant liquid until it is called for by the metering device.
When the purpose of the device shown in FIG. 1 is merely to cool and/or dry air, the water condensing on the evaporator is allowed to simply drain away. When the purpose is to collect potable water, a reservoir is placed beneath the evaporator. Care must be taken to assure that the water is obtained in potable condition and that it remains so after collection. This is accomplished by manufacturing the evaporator, the reservoir and any other parts of the device that come in contact with the moist air or the condensed water, from non-contaminating materials or to coat or line potentially contaminating materials with the non-contaminating kind. Examples of such materials are stainless steel, glass and a broad range of polymeric materials such as PVC, Teflon(copyright) and the like. To ensure that collected water remains potable, such procedures as irradiating the water with ultraviolet light, bubbling ozone through it, adding iodine or other chemical anti-microbial agents, etc., are often used.
The device described above works reasonably well at ambient air temperatures above about 55xc2x0 F. A problem arises, however, when the air temperature is below about 55xc2x0 F. such as might be encountered in refrigeration units, fruit and vegetable produce drying rooms and meat storage lockers or when potable water is needed and the ambient temperature is less than about 55xc2x0 F., such as at night or in winter. The problem is that, as water vapor, which is at about 55xc2x0 F. or below, is condensed on the evaporator surface of the device in FIG. 1, it is rapidly cooled further because the evaporator surface is usually at a temperature substantially below 32xc2x0 F. due to the thermodynamic characteristics of commonly used refrigerants and the normal operating modes of such devices. At 32xc2x0 F. or below, the condensate freezes, forming ice on the evaporator. At ambient air temperatures below about 55xc2x0 F., air that is in contact with the water on the surface of the evaporator cannot supply sufficient additional heat to counteract this freezing condition. As a result, ice builds up on the evaporator surface and acts as an insulator, isolating the evaporator surface from the moisture-laden air and thereby interfering with the operation of the device. When this occurs, the usual remedy is to turn off the compressor, shutting down the device, until the ice melts. The result is that the device of FIG. 1 is extremely inefficient at ambient air temperatures below about 55xc2x0 F.
One approach that is employed to avoid evaporator icing is to simply run the device at higher refrigerant temperatures. This, however, limits the cooling capability of the device. Furthermore, if the goal is to remove water from the ambient air, it is preferred that the device be run as cold as possible so that the air is cooled to as close to the freezing point of water as possible since the colder the air, the less water it can retain. Running the device at a higher refrigerant temperature is thus inefficient since it leaves water in the air.
An approach employed to reduce inefficiency due to down time is to use multiple devices and to alternate use so that when the evaporator of one device has iced up, it can be shut down and another device started up. This, however, is an expensive, not to mention space-consuming, resolution.
What is needed is a device and method that performs a refrigeration cycle, in particular at temperatures below about 55xc2x0 F., without evaporator icing. The present invention provides such a device.
The present invention relates to a device that operates in a refrigeration cycle at temperatures below about 55xc2x0 F. while avoiding ice formation on its evaporator assembly. Of course, the device and method herein will work equally well at any ambient air temperature but it is at temperatures below about 55xc2x0 F. that icing is particularly problematic and the device herein is of the greatest utility.
A presently preferred embodiment of this invention is a device for avoiding evaporator icing at ambient air temperatures from about 32.5xc2x0 F. to about 55xc2x0 F. While being equally effective for preventing evaporator icing at temperatures below 32.5xc2x0 F., at such temperatures air holds very little moisture and the problem of evaporator icing, although still present, occurs more slowly and is less of a concern except when uninterrupted long term operation of the device is desired.
To accomplish the above, the device of this invention comprises a hot gas bypass that permits the output of a compressor, i.e., hot, high pressure gas, to be mixed with the output of a metering means, i.e., cool, low pressure liquid, in a controlled manner, at a location proximate to the output of the metering means. Examples of useful metering means are a simple orifice, an orifice with a floating piston, a capillary tube or a thermostatic expansion valve (TXV). The hot gas bypass is in communication with a controller. The controller is also in communication with a temperature sensor. In a presently preferred embodiment of this invention, the temperature sensor is located proximate to the inlet of the evaporator. The temperature sensor measures the temperature of the low pressure liquid entering the evaporator and provides a signal corresponding to that temperature to the controller. The controller comprises a low temperature set point and a high temperature set point. When the temperature sensor sends a temperature signal to the controller that is at or below the low temperature set point, the controller causes the hot gas bypass to open, permitting hot gas from the outlet of the compressor to mix with the cool liquid entering the evaporator, warming it. The warmer liquid requires less heat energy to vaporize and does not absorb as much heat from the air flowing over the outer surface of the evaporator or from the water condensing on the evaporator. Thus, water on the evaporator is not cooled to the freezing point and no ice forms. When the temperature sensor sends a signal to the controller that is at or above the high temperature set point, the controller causes the hot gas bypass to close. Thus, the hot gas bypass provides precise control, within fractions of a degree F, of the temperature of the liquid flowing through the evaporator and, therefore, of the evaporator surface and of water condensing on that surface. The temperature of the water on the surface of the evaporator can be maintained at a temperature barely above freezing without ice formation which results in maximum efficiency both in terms of extracting as much water as possible from the ambient air in contact with the surface of the evaporator and avoidance of down-time due to evaporator freezing.
While, as noted above, in a presently preferred embodiment, the temperature sensor is located proximate to the inlet of the evaporator, it may be placed at any location in the vicinity of, or even on, the evaporator where it is desired to measure the temperature of the liquid or gas at the evaporator. Furthermore, it is within the scope of this invention that the temperature sensor may be split into two separate temperature sensors, one of which measures the temperature at one location, for example, without limitation, at the inlet to the evaporator and one of which measures the temperature at a different location, for example, likewise without limitation, at the outlet of the evaporator. In this case, one of the temperatures is sent to the controller as the high temperature and the other is sent to the controller as the low temperature where these temperatures are compared with the high temperature set point and the low temperature set point, respectively. The controller then causes the hot gas bypass to open and close as described above.
A single hot gas bypass may be used in the device and method of this invention or a plurality of hot gas bypasses may be used. If a single hot gas bypass is used, its outlet is preferably connect to a location between the outlet of the metering means and the inlet to the evaporator. If a plurality of hot gas bypasses are used, it is likewise preferred that one of them has its outlet connected to a location between the metering means and the evaporator. The others, however, may have their outlets connected to any point on the evaporator assembly. That is, a temperature sensor might be located half way along the evaporator assembly and the outlet from the hot gas bypass may be connected to the evaporator a short distance upstream, i.e., in the direction counter to refrigerant flow in the system, of the temperature sensor.
The above described device of this invention will accomplish the purpose of this invention, i.e., operate in a refrigeration cycle while avoiding evaporator icing, at virtually any temperature, however, it is particularly effective under extreme conditions, i.e., ambient air temperatures below 55xc2x0 F., even below 32xc2x0 F., and during very long periods of continuous operation. At temperatures above about 55xc2x0 F., however, a device of this invention may further comprise, as the metering means, a thermal expansion valve (TXV) that is controlled by a temperature-sensing bulb assembly. A TXV can also control the temperature of liquid entering an evaporator but does so by controlling the amount of liquid that reaches the evaporator at any given time rather than by injecting hot gas into the liquid stream entering the evaporator. Thus, under less extreme conditions, that is, at temperatures above about 55xc2x0 F., a TXV can reduce some of the work load on the hot gas bypass by providing an additional degree of control of the temperature of liquid entering the evaporator. TXVs are well-known in the art as are the temperature sensing bulbs that control them. However, the temperature-sensing assembly described herein, which provides a degree of TXV control precision consummate with a device of this invention, i.e., that allows operation of the device without icing of the evaporator, is novel.
The temperature-sensing assembly comprises a thermal well in which a standard temperature-sensing bulb is placed, the thermal well being constructed so as to rapidly transmit small changes in the temperature of the gas exiting the evaporator outlet to the temperature-sensing bulb which can then precisely control the operation of the TXV. To accomplish this, the thermal well has a baffled annular space through which the liquid refrigerant passes before entering the evaporator. The baffle increases the residence time in the annular space to ensure that temperature changes in the liquid refrigerant are transmitted to the wall of the thermal well. The space between the temperature-sensing bulb and the wall of the thermal well is filled with a highly thermoconductive material that efficiently and rapidly transmits changes in refrigerant liquid temperature from the wall of the thermal well to the temperature-sensing bulb.
A device of this invention may also comprise one or more frost sensors at various points on the exterior surface of the evaporator as an added icing deterrent during extreme temperature or prolonged continuous operation conditions. Frost detectors are well-known in the art and would be used without modification with a device of this invention. However, rather than operate in the normal fashion of conventional frost detectors and simply turn off the compressor if frost is detected, in the present invention, the frost detectors are in communication with the controller. When the controller receives a signal indicating that frost is beginning to form on a portion of the surface of the evaporator, it causes the hot gas bypass to open briefly and provide a small charge of hot gas to the liquid entering the evaporator. These bursts of hot gas would continue until the frost sensor stops sending a frost signal.
The device of this invention may also comprise a plurality of evaporators. The evaporators may be connected in parallel off of a manifold which in turn may be connected to the outlet of the metering means, the outlet of the condenser or the outlet of the compressor. In each of these cases, the requisite additional elements of the device would be connected to the manifold. That is, for example, if the manifold is connected to the outlet of the compressor, then a condenser and a metering means would be included between the manifold and each evaporator. Each evaporator can then be connected to its own hot gas bypass, its own temperature sensor and controller and, optionally, its own TXV and temperature-sensing assembly. Or a plurality of evaporators may be connected to a manifold which, in turn, is connected to a single hot gas bypass/temperature sensor/controller/ TXV/temperature-sensing assembly.
Thus, in one aspect, this invention is related to a device that permits the operation of a refrigeration cycle while avoiding evaporator icing, comprising:
a compressor having an inlet and an outlet;
a condenser, having an inlet and an outlet, wherein the condenser inlet is operatively coupled to the outlet of the compressor;
a metering means, having an inlet and an outlet, wherein the inlet of the metering means is operatively coupled to the outlet of the condenser;
an evaporator, having an inlet and an outlet, wherein the evaporator inlet is operatively coupled to the outlet of the metering means and the outlet of the evaporator is operatively coupled to the inlet of the compressor;
a hot gas bypass means, having an inlet, an outlet, an open position and a closed position, wherein the hot gas bypass means inlet is operatively coupled to the outlet of the compressor and the outlet of the hot gas bypass means is operatively coupled to the outlet of the metering means;
a temperature-sensing means operatively coupled to the inlet of the evaporator and to a controller, the temperature-sensing means sensing the temperature of a circulating liquid refrigerant at the inlet of the evaporator and deriving a temperature signal corresponding to that temperature;
a controller that received the temperature signal from the temperature-sensing means, the controller comprising a high temperature set point and a low temperature set point such that, when the controller receives a temperature signal from the temperature sensing means that is at or below the low temperature set point, the controller sends an open signal to the hot gas bypass means and when the controller receives a temperature signal from the temperature sensing means that is at or above the high temperature set point, the controller sends a close signal to the hot gas bypass means; and,
a refrigerant that circulates from the compressor to the condenser to the metering means to the evaporator and back to the compressor in a refrigeration cycle.
In another aspect, this invention relates to the above device wherein the metering means comprises a thermostatic expansion valve.
In a still further aspect of this invention, the thermostatic expansion valve comprises a temperature-sensing assembly.
In an aspect of this invention, the temperature sensing assembly comprises:
a double-walled container comprising an inner member and an outer member;
a first space disposed between the inner member and the outer member;
a second inner space circumscribed by the inner member;
an inlet disposed proximate to, in and through a first end of the outer member, the inlet being operatively coupled to the outlet of the evaporator;
an outlet disposed proximate to, in and through a second end opposite the first end of the outer member, the outlet being operatively coupled to the inlet of the compressor;
a baffle disposed in the first space and extending from proximate to the first end of the outer member to proximate to the second end of the outer member;
a temperature sensing bulb disposed in the inner space, the temperature sensing bulb being operatively coupled to the thermostatic expansion valve; and,
a thermal compound also disposed in the inner space, the thermal compound being in contact with the inner member and the temperature-sensing bulb.
The hot gas bypass means comprises a hot gas bypass valve in another aspect of this invention.
The hot gas bypass valve comprises a solenoid in an aspect of this invention.
In a still further aspect of this invention, the temperature-sensing means comprises a thermocouple.
It is an aspect of this invention that the controller comprises a microprocessor.
An aspect of this invention relates to the above device wherein a water reservoir is included to catch water flowing off of the evaporator.
In an aspect of this invention, when the above device includes a water reservoir, both the reservoir and the evaporator comprise one or more noncontaminating materials.
It is also an aspect of this invention that, when the device includes a water reservoir, the device also comprises an ozone source, which is capable of delivering ozone to the water in the reservoir.
The ozone source is an electrostatic ozone generator in a further aspect of this invention.
The ozone source is connected to a fritted glass dispersion device that is capable of producing ozone in very small bubbles that can then be dispersed through the water in the water reservoir.
A further aspect of this invention is a method for preventing evaporator icing during operation of a refrigeration cycle, comprising:
providing a refrigerant gas;
providing a compressor, having an inlet and an outlet, wherein low temperature, low pressure refrigerant gas enters the compressor inlet, is compressed therein and then is expelled from the outlet of the compressor as a high temperature, high pressure refrigerant gas;
providing a condenser, having an inlet and an outlet, the inlet of the condenser being operatively coupled to the outlet of the compressor, wherein the high temperature, high pressure refrigerant gas enters the condenser inlet, releases heat energy therein to external air passing over an outer surface of the condenser, is condensed and is expelled from the outlet of the condenser as a low temperature, high pressure refrigerant liquid;
providing a metering device, having an inlet and an outlet, the inlet of the meter being operatively coupled to the outlet of the condenser, wherein the low temperature, high pressure refrigerant liquid enters the metering means inlet and is controllably discharged from the metering means outlet as a low temperature, low pressure refrigerant liquid;
providing an evaporator, having an inlet and an outlet, the inlet of the evaporator being operatively coupled to the outlet of the metering means, wherein the low temperature, low pressure refrigerant liquid enters the evaporator inlet, absorbs heat from ambient air, which may or may not contain water vapor and which is at a higher temperature than the low temperature refrigerant liquid, through an outer surface of the evaporator, reducing an air temperature to below the dew point of the air, if it contains water, as a result of which the water vapor condenses onto the surface of the evaporator while the refrigerant liquid is vaporized to a low temperature, low pressure refrigerant gas which is expelled from the outlet of the evaporator and is drawn into the inlet of the compressor to begin another cycle;
providing a hot gas bypass means, having an inlet, an outlet, an open position and a closed position, the hot gas bypass means inlet being operatively coupled to the outlet of the compressor, the hot gas bypass means outlet being operatively coupled to the outlet of the metering means;
providing a temperature-sensing means operatively coupled to the evaporator inlet;
providing a controller operatively coupled to the temperature-sensing means and to the hot gas bypass means,
wherein, the temperature-sensing means measures a temperature of the refrigerant liquid entering the evaporator and sends a temperature signal corresponding to that temperature to the controller, wherein if the temperature signal is at or below a low temperature set point, the controller sends an open signal to the hot gas bypass means permitting high temperature, high pressure refrigerant gas from the outlet of the compressor to mix with the low temperature, low pressure refrigerant liquid at the outlet of the metering means until the controller means receives a temperature signal from the temperature-sensing means that is at or above a high temperature set point at which time the controller sends a close signal to the hot gas bypass means; and,
circulating the refrigerant from the compressor to the condenser to the metering means to the evaporator and thence back to the compressor in a refrigeration cycle.
An aspect of this invention is the above method in which the metering means comprises a thermostatic expansion valve.
The thermostatic expansion valve further comprises a temperature-sensing assembly in the above method in an aspect of this invention.
The temperature-sensing assembly comprises:
a double-walled container comprising an inner member and an outer member;
a first space disposed between the inner member and the outer member;
a second inner space circumscribed by the inner member;
an inlet disposed proximate to, in and through a first end of the outer member, the inlet being operatively coupled to the outlet of the evaporator;
an outlet disposed proximate to, in and through a second end opposite the first end of the outer member, the outlet being operatively coupled to the inlet of the compressor;
a baffle disposed in the first space and extending from proximate to the first end of the outer member to proximate to the second end of the outer member;
a temperature sensing bulb disposed in the inner space, the temperature sensing bulb being operatively coupled to the thermostatic expansion valve; and,
a thermal compound also disposed in the inner space, the thermal compound being in contact with the inner member and the temperature-sensing bulb, in another aspect of the above method of this invention.
In the above method, the hot gas bypass means comprises a hot gas bypass valve in an aspect of this invention.
The hot gas bypass valve comprises a solenoid in an aspect of the above method of this invention.
It is an aspect of this invention that, in the above method, the temperature-sensing means comprises a thermocouple.
It is also an aspect of this invention that, in the above method, the controller comprises a microprocessor.
In the above method, a reservoir is positioned so as to collect water flowing off of the evaporator in another aspect of this invention.
The reservoir and the evaporator comprise one or more noncontaminating materials in the above method in a still further aspect of this invention.
In the above method, it is an aspect of this invention that an ozone source is placed in the reservoir such that ozone from the ozone source can be dispersed through water collecting therein.
Dispersing ozone through the water is accomplished using a fritted glass dispersion device in a further aspect of this invention.